The present invention generally relates to a locomotive diesel engine and, more specifically, to a pressure balanced exhaust gas recirculation (“EGR”) assembly for a locomotive diesel engine having an EGR system. The present invention EGR assembly may be implemented in a locomotive two-stroke uniflow scavenged diesel engine.
FIG. 1 illustrates a locomotive 100 including a conventional uniflow two-stroke diesel engine system 150. As shown in FIGS. 2a and 2b, the locomotive diesel engine system 150 of FIG. 1 includes a conventional air system. Referring concurrently to both FIGS. 2a and 2b, the locomotive diesel engine system 150 generally comprises a turbocharger 200 having a compressor 202 and a turbine 204 which provides compressed air to an engine 206 having an airbox 208, power assemblies 210, an exhaust manifold 212, and a crankcase 214. In a typical locomotive diesel engine system 150, the turbocharger 200 increases the power density of the engine 206 by compressing and increasing the amount of air transferred to the engine 206.
More specifically, the turbocharger 200 draws air from the atmosphere 216, which is filtered using a conventional air filter 218. The filtered air is compressed by a compressor 202. The compressor 202 is powered by a turbine 204, as will be discussed in further detail below. A larger portion of the compressed air (or charge air) is transferred to an aftercooler (or otherwise referred to as a heat exchanger, charge air cooler, or intercooler) 220 where the charge air is cooled to a select temperature. Another smaller portion of the compressed air is transferred to a crankcase ventilation oil separator 222 which evacuates the crankcase 214 in the engine; entrains crankcase gas; and filters entrained crankcase oil before releasing the mixture of crankcase gas and compressed air into the atmosphere 216.
The cooled charge air from the aftercooler 220 enters the engine 206 via an airbox 208. The decrease in charge air intake temperature provides a denser intake charge to the engine which reduces NOX emissions while improving fuel economy. The airbox 208 is a single enclosure, which distributes the cooled air to a plurality of cylinders. The combustion cycle of a diesel engine includes what is referred to as scavenging and mixing processes. During the scavenging and mixing process, a positive pressure gradient is maintained from the intake port of the airbox 208 to the exhaust manifold 212 such that the cooled charge air from the airbox 208 charges the cylinders and scavenges most of the combusted gas from the previous combustion cycle.
More specifically, during the scavenging process in the power assembly 210, the cooled charge air enters one end of a cylinder controlled by an associated piston and intake ports. The cooled charge air mixes with a small amount of combusted gas remaining from the previous cycle. At the same time, the larger amount of combusted gas exits the other end of the cylinder via four exhaust valves and enters the exhaust manifold 212 as exhaust gas. The control of these scavenging and mixing processes is instrumental in emissions reduction as well as in achieving desired levels of fuel economy.
Exhaust gases from the combustion cycle exit the engine 206 via an exhaust manifold 212. The exhaust gas flow from the engine 206 is used to power the turbine 204 of the turbocharger 200, and thereby the compressor 202 of the turbocharger 200. After powering the turbine 204 of the turbocharger 200, the exhaust gases are released into the atmosphere 216 via an exhaust stack 224 or silencer.
The exhaust gases released into the atmosphere by a locomotive diesel engine include particulates, nitrogen oxides (NOX) and other pollutants. Legislation has been passed to reduce the amount of pollutants that may be released into the atmosphere. Traditional systems have been implemented which reduce these pollutants, but at the expense of fuel efficiency. Accordingly, it is an object of the present invention to provide a system which reduces the amount of pollutants released by the diesel engine while achieving desired fuel efficiency. It is a further object of the present invention to provide an EGR system for a uniflow two-stroke diesel engine, which manages the aforementioned scavenging and mixing processes to reduce NOX while achieving desired fuel economy.
As described with regard to the various aspects of the present invention, emissions reduction may be achieved by recirculating some of the exhaust gas back through the engine. Major constituents of exhaust gas that are recirculated include N2, CO2, and water vapor, which affect the combustion process through dilution and thermal effects. The dilution effect is caused by the reduction in the concentration of oxygen in intake air. The thermal effect is caused by increasing the specific heat capacity of the charge.
Because flow of exhaust gas through the EGR system depends on internal pressure therein, it is important that internal pressure be high. However, if the internal pressure of certain EGR system parts becomes higher than the external pressure of those parts, the internal pressure will cause deformation to the system housing. Therefore, it is an object of the present invention pressure balance EGR assembly to equalize internal pressure across the EGR system and prevent deformation of EGR system parts.
The various embodiments of the present invention EGR system are able to exceed what is referred in the industry as the Environmental Protection Agency's (EPA) Tier II (40 CFR 92) and Tier III (40 CFR 1033) NOX emission requirements, as well as the more stringent European Commission (EURO) Tier IIIb NOX emission requirements. These various emission requirements are cited by reference herein and made a part of this patent application.
Locomotives must also be able operate within specific length, width, and height constraints. For example, the length of the locomotive must be below that which is necessary for it to negotiate track curvatures or a minimum track radius. In another example, the width and height of the locomotive must be below that which is necessary for it to clear tunnels or overhead obstructions. Locomotives have been designed to utilize all space available within these size constraints. Therefore, locomotives have limited space available for adding new system components thereon. Accordingly, it also an object of the present invention to provide a system, which may be placed within the limited size constraints of the locomotive and preferably within the same general framework of an existing locomotive.